In the Fischer-Tropsch reaction synthesis gas is reacted in the presence of a heterogeneous catalyst to give a hydrocarbon mixture having a relatively broad molecular weight distribution. This product comprises predominantly straight chain saturated hydrocarbons which typically have a chain length of more than 5 carbon atoms. The reaction is highly exothermic and therefore heat removal is one of the primary constraints of all Fischer-Tropsch processes.
It has recently been found that a Fischer-Tropsch process may be operated by contacting synthesis gas with a suspension of a catalyst in a liquid medium in a system comprising at least one high shear mixing zone and a reactor vessel. This process is described in WO 0138269 (PCT patent application number GB 0004444) which is herein incorporated by reference. It has now been found that a Fischer-Tropsch catalyst comprising cobalt can be treated with a reducing gas to provide a highly active catalyst with increased selectivity to liquid hydrocarbons.